1. Field of the Invention
The present invention relates to a protective circuit of a battery pack. More particularly, the present invention relates to a protective circuit of a battery pack, capable of detecting disconnection of a sensing wire, which senses a voltage of a battery cell, while preventing overcharge of the battery cell.
2. Description of the Related Art
As generally known in the art, a battery cell is typically not used as a power source for a notebook personal computer and the like because the battery cell has low capacity and operational voltage. Thus, a battery pack or a battery cell module including a plurality of battery cells coupled to each other in series is used as a power source for the notebook personal computer.
Such a battery pack is assembled with a protective circuit in order to control the charge/discharge state of the battery cell while protecting the battery pack from various hazards derived from the overcharge or over-discharge of the battery cell. In addition, a sensing wire is coupled to the protective circuit in order to detect the voltage of each battery cell. For instance, when the battery pack includes three battery cells coupled to each other in series, four sensing wires are required. In this case, a first sensing wire is coupled to a negative electrode of a first battery cell in order to detect a minimum voltage, a second sensing wire is coupled between a positive electrode of the first battery cell and a negative electrode of the second battery cell so as to detect a maximum voltage of the first battery cell (or, a minimum voltage of the second battery cell), a third sensing wire is coupled between a positive electrode of the second battery cell and a negative electrode of the third battery cell so as to detect a maximum voltage of the second battery cell (or, a minimum voltage of the third battery cell), and a fourth wire is coupled to a positive electrode of the third battery cell in order to detect a maximum voltage of the third battery cell.
According to the circuit structure having the above construction, the voltage of the first battery cell is detected by means of first and second wires, the voltage of the second battery cell is detected by means of second and third wires, and the voltage of the third battery cell is detected by means of third and fourth wires, respectively.
Therefore, the voltage of each battery cell can be detected, so the overcharge of all battery cells or a specific battery cell can be detected. If the overcharge of the battery cell is detected, the charge operation for the battery cell is instantly stopped.
However, the conventional protective circuit presents a problem in that there is no apparatus or method for detecting disconnection of a specific sensing wire. For instance, if the second wire is disconnected, the total voltage of the battery cells can be detected by means of the first and fourth wires, but the voltage of the first battery cell cannot be detected. That is, an average voltage value of the first and second battery cells is only detected by means of the first and third wires. In this case, it is impossible to precisely detect the overcharge of the first battery cell even if the first battery cell has been subject to the overcharge state. Accordingly, the first battery cell may be continuously overcharged, thereby causing explosion or ignition of the first battery cell. In addition, it is also difficult to precisely detect the voltage of the second battery cell, so that the secondary battery cell may also be subject to the overcharge.